The answer: not many. Running this on /usr/share/dict/words yields a paltry 12 words; all of which, “ravine” excepted, are four letters or less. We get slightly better results running it on the 390,583-word british-english-huge file from 12dicts (which I keep installed for exactly this sort of tomfoolery). On the other hand, some of the extra words are quite obscure. The full list: